A multiple-antenna (Multiple-Input Multiple-Output, MIMO) technology has been widely applied to wireless communications systems to expand a system capacity and ensure cell coverage. For example, multiple-antenna-based transmit diversity, open-loop/closed-loop spatial multiplexing, and DM-RS-based multi-stream transmission are used for downlink in a Long Term Evolution (Long Term Evolution, LTE) system. The demodulation reference signal (Demodulation Reference Signal, DM-RS)-based multi-stream transmission is a main transmission mode in an LTE-A system and a subsequent system. A procedure of the DM-RS-based multi-stream transmission is as follows: UE first performs channel measurement according to a channel state indicator-reference signal (Channel Status Indicator Reference Signal, CSI-RS) configured by an evolved NodeB (evolved Node B, eNB). A measurement result includes a rank indication (Rank Indication, RI), a precoding matrix corresponding to the rank indication, and a channel quality indicator (Channel Quality Indication, CQI) corresponding to the rank indication and the precoding matrix. Then the UE feeds back the measurement result to the eNB. The eNB performs downlink scheduling according to the measurement result fed back by the UE, and sends a physical downlink shared channel (Physical Downlink Shared Channel, PDSCH) to the UE according to a scheduling result by using a DM-RS. Currently, two-dimensional beamforming is used for the DM-RS-based multi-stream transmission. That is, a transmit antenna is placed only horizontally, and can generate a beam only in a horizontal direction.
To further improve multiple-antenna system performance, a two-dimensional antenna configuration is being researched in the LTE Rel-12 standard. That is, antennas are placed in both the horizontal direction and a vertical direction, so that beamforming can be performed in both the horizontal direction and the vertical direction. This is referred to as three-dimensional beamforming. Therefore, in comparison with the current two-dimensional beamforming, a degree of freedom in the vertical direction is added. In this way, multiplexing can be performed for more users on a same time-frequency resource. Different users are distinguished from each other according to a beam in the vertical direction or the horizontal direction, so as to increase resource utilization or spectral efficiency.
For the 3D MIMO, in the prior art, user equipment (User Equipment, UE) feeds back a CQI, or a channel quality indicator (Channel Quality Indicator, CQI) and a precoding matrix indicator (Precoding Matrix Indicator, PMI) on a physical uplink control channel (Physical Uplink Control Channel, PUCCH). A specific feedback mode is PUCCH X1-X2. When a value of X1 is 1, the CQI that is fed back is a bandwidth CQI; or when a value of X1 is 2, the CQI that is fed back is a subband CQI. When a value of X2 is 0, the PMI is not fed back; or when a value of X2 is 1, the PMI is fed back, and the PMI indicates a precoding matrix in a preset codebook.
However, for a beamformed CSI-RS mechanism in LTE Rel-13, where Rel-13 is Release 13, a prior-art feedback mode does not consider reporting a newly added beamforming indication (Beamforming Indication, BI). Therefore, the existing PUCCH feedback mode cannot be applied to the beamformed CSI-RS mechanism in Rel-13. In addition, because an antenna configuration is changed into a two-dimensional, a new 2D codebook is used in a non-precoded CSI-RS mechanism in Rel-13. Because the existing feedback mode cannot be used, a new PUCCH feedback mode applicable to a latest 2D codebook is required.